Synthesis and coordination properties of new macrocyclic ligands: equilibrium studies and crystal structures

The synthesis and characterization of two new macrocyclic ligands, the bis-macrocyclic compound 2,6-bis(1,4,13-triaza-7,10-dioxacyclopentadec-1-ylmethyl) phenol (L) and 38-methoxy-1,4,13,16,19,28-hexaaza-7,10,22,25-tetraoxatricyclo[14.14.7.1(32,36)] octatriconta-32,34, Delta(36,38)-triene (L1) are reported. Equilibrium studies of basicity and coordination properties toward metal ions such as Cu(II), Zn(II), Cd(II) and Pb(II) were performed for ligand L by potentiometric measurements in aqueous solution (298.1+/-0.1 K, I=0.15 mol dm(-3)). L behaves as a hexaprotic base (logK(1)=10.93, logK(2)=9.70, logK(3)=8.79, logK(4)=8.05, logK(5)=6.83, logK(6)=2.55). All metal ions form stable mono- and dinuclear complexes: logK(MLH -1)=25.61 for Cu(II), 15.37 for Zn(II), 12.58 for Cd(II) and 13.79 for Pb(II); logK(M 2 LH -1)=31.61 for Cu(II), 23.38 for Zn(II), 24.49 for Cd(II) and 23.68 for Pb(II). All these dinuclear species show a great tendency to add the OH- group: the equilibrium constant for the addition reaction was found to be log KM 2 LH -1 OH=4.77 for Cu(II), 5.66 for Zn(II), 2.8 for Cd(II) and 3.18 for Pb(II). In the case of Ni(II), kinetic inertness prevents the possibility of solution studies. The dinuclear solid adducts [Ni2H-1L(N-3)(3)].EtOH and [Cu2H-1L(N-3)](ClO4)(2) were characterized by X-ray analysis.